The present invention relates to DC brushless motors, and in particular to a commutation and velocity control system for a brushless DC motor.
Brushless DC motors are in widespread use. A brushless DC motor employs a permanently magnetized rotor and electronic commutation to switch current to appropriate stator windings to cause the rotor to rotate to follow switched magnetic poles in the stator windings. Brushless DC motors may be commutated by signals generated from the rotational velocity and position of the rotor to cause the appropriate stator winding to be switched to sustain rotation. Furthermore, brushless DC motors may be commutated by an external frequency source to cause the rotor to rotate at a rotational velocity synchronous with the external signal source. Mechanisms for detecting the rotational velocity and position of the rotor include resolver windings, Hall effect devices, optical position sensors, etc.
Brushless DC motors often achieve brushless commutation by the use of the resolver that is rotationally coupled to an armature shaft and a pair of resolver windings, respectively producing output signals sineθ and cosineθ, where θ is the angular position of the shaft, which are used to control the windings for driving the armature. From these position signals, velocity must be derived in order to control the commutation.
There is a need for a simplified commutation and velocity control system for a brushless DC motor.